The Appeal of Plaster

Plaster, as an element in architecture and decor, seems like an anachronism. In a world possessed of super-composites and ultra-alloys, plaster might be seen as a quaint holdover originally used because architects just didn’t have anything better.

With the unearthing of the Turkish proto-city Catalhöyük in the 1950’s and 60’s, lime frescoes -- murals painted with water colours directly onto wet plaster -- were discovered. These depictions of hunting, volcanoes and geometric patterns proved that plaster has been used by humans for nearly 10,000 years, back into the Neolithic period.

Ten millennia worth of use. And the qualities of plaster go far beyond their early discovery.

Simplicity

Certainly the concept of combining earthen materials with water to produce a hardened substance is a common one. The everyday presence of cements and mortars and clay and drywall spackle has made them almost unnoticed by anyone except the craftspeople and construction workers who work with it.

Ease of Manufacture and Use

At various times in various places, innovative societies stepped up from mud and clay plasters to lime and gypsum. They discovered that heating those materials allowed them to crush them into powder. They then mixed the powder with water to create a slurry. The slurry could be poured into a container to make almost any desired shape; sculptures and decor that were rock-hard.

These “calcined“ plasters may have been accidentally created during the use of gypsum and lime rocks in the structure of a pottery kiln. The heat would have driven off much of the water in gypsum and the carbon dioxide in lime leaving easily crumbled leftovers. Quenching the kiln’s embers with water could have spilled on the new plasters. Observant potters would notice a powder that hardened unexpectedly.

Durability

With gypsum-based plaster, the adding of water followed by approximately 72 hours of drying, rehydrates the powder to the same state as raw gypsum. And as such, it’s as durable as rock. Granted, not a very hard rock -- gypsum is only a two out of ten on the Moh’s scale of hardness -- but it doesn’t need a lot of care to last for, literally, thousands of years.

Inside Egyptian pyramids, 4,000 year old plaster remains hard and in the place it was applied. Their gypsum plaster is identical to the Plaster of Paris used in the present day.

Plasters, other than those made with clay, have respectable compressive strength and its tensile, torsional, and shear strengths can be improved slightly with the addition of fibers into the mix. Reeds, grasses, and horse hair in the past have now been replaced with fiberglass.

And Everything Else

The first users of plaster were probably thankful enough for its ability to keep out the elements .In later millenia, they learned that plaster is fire resistant and provides some insulation from noise. Artisans and craftspeople admired that it sets from liquid to solid in minutes and that it expands only slightly as it dries -- allowing every detail from molds to be represented in the finished surface.

Before the invention of electric light, children afraid of the dark owed a few less nightmares to the presence of plaster; if its surface were burnished, it reflected more light from flickering tapers and low-efficiency oil lamps. 

Because it’s so ubiquitous, common, and taken for granted, the last, most subjective trait might be the most forgotten. Its beauty.